drivers/net/dummy.c

   1 /* dummy.c: a dummy net driver
   2
   3         The purpose of this driver is to provide a device to point a
   4         route through, but not to actually transmit packets.
   5
   6         Why?  If you have a machine whose only connection is an occasional
   7         PPP/SLIP/PLIP link, you can only connect to your own hostname
   8         when the link is up.  Otherwise you have to use localhost.
   9         This isn't very consistent.
  10
  11         One solution is to set up a dummy link using PPP/SLIP/PLIP,
  12         but this seems (to me) too much overhead for too little gain.
  13         This driver provides a small alternative. Thus you can do
  14
  15         [when not running slip]
  16                 ifconfig dummy slip.addr.ess.here up
  17         [to go to slip]
  18                 ifconfig dummy down
  19                 dip whatever
  20
  21         This was written by looking at Donald Becker's skeleton driver
  22         and the loopback driver.  I then threw away anything that didn't
  23         apply!  Thanks to Alan Cox for the key clue on what to do with
  24         misguided packets.
  25
  26                         Nick Holloway, 27th May 1994
  27         [I tweaked this explanation a little but that's all]
  28                         Alan Cox, 30th May 1994
  29 */
  30
  31 #include <linux/module.h>
  32 #include <linux/kernel.h>
  33 #include <linux/netdevice.h>
  34 #include <linux/etherdevice.h>
  35 #include <linux/init.h>
  36 #include <linux/moduleparam.h>
  37 #include <linux/rtnetlink.h>
  38 #include <net/rtnetlink.h>
  39
  40 static int numdummies = 1;
  41
  42 static int dummy_xmit(struct sk_buff *skb, struct net_device *dev);
  43
  44 static int dummy_set_address(struct net_device *dev, void *p)
  45 {
  46         struct sockaddr *sa = p;
  47
  48         if (!is_valid_ether_addr(sa->sa_data))
  49                 return -EADDRNOTAVAIL;
  50
  51         memcpy(dev->dev_addr, sa->sa_data, ETH_ALEN);
  52         return 0;
  53 }
  54
  55 /* fake multicast ability */
  56 static void set_multicast_list(struct net_device *dev)
  57 {
  58 }
  59
  60 static const struct net_device_ops dummy_netdev_ops = {
  61         .ndo_start_xmit         = dummy_xmit,
  62         .ndo_validate_addr      = eth_validate_addr,
  63         .ndo_set_multicast_list = set_multicast_list,
  64         .ndo_set_mac_address    = dummy_set_address,
  65 };
  66
  67 static void dummy_setup(struct net_device *dev)
  68 {
  69         ether_setup(dev);
  70
  71         /* Initialize the device structure. */
  72         dev->netdev_ops = &dummy_netdev_ops;
  73         dev->destructor = free_netdev;
  74
  75         /* Fill in device structure with ethernet-generic values. */
  76         dev->tx_queue_len = 0;
  77         dev->flags |= IFF_NOARP;
  78         dev->flags &= ~IFF_MULTICAST;
  79         random_ether_addr(dev->dev_addr);
  80 }
  81
  82 static int dummy_xmit(struct sk_buff *skb, struct net_device *dev)
  83 {
  84         dev->stats.tx_packets++;
  85         dev->stats.tx_bytes += skb->len;
  86
  87         dev_kfree_skb(skb);
  88         return 0;
  89 }
  90
  91 static int dummy_validate(struct nlattr *tb[], struct nlattr *data[])
  92 {
  93         if (tb[IFLA_ADDRESS]) {
  94                 if (nla_len(tb[IFLA_ADDRESS]) != ETH_ALEN)
  95                         return -EINVAL;
  96                 if (!is_valid_ether_addr(nla_data(tb[IFLA_ADDRESS])))
  97                         return -EADDRNOTAVAIL;
  98         }
  99         return 0;
 100 }
 101
 102 static struct rtnl_link_ops dummy_link_ops __read_mostly = {
 103         .kind           = "dummy",
 104         .setup          = dummy_setup,
 105         .validate       = dummy_validate,
 106 };
 107
 108 /* Number of dummy devices to be set up by this module. */
 109 module_param(numdummies, int, 0);
 110 MODULE_PARM_DESC(numdummies, "Number of dummy pseudo devices");
 111
 112 static int __init dummy_init_one(void)
 113 {
 114         struct net_device *dev_dummy;
 115         int err;
 116
 117         dev_dummy = alloc_netdev(0, "dummy%d", dummy_setup);
 118         if (!dev_dummy)
 119                 return -ENOMEM;
 120
 121         err = dev_alloc_name(dev_dummy, dev_dummy->name);
 122         if (err < 0)
 123                 goto err;
 124
 125         dev_dummy->rtnl_link_ops = &dummy_link_ops;
 126         err = register_netdevice(dev_dummy);
 127         if (err < 0)
 128                 goto err;
 129         return 0;
 130
 131 err:
 132         free_netdev(dev_dummy);
 133         return err;
 134 }
 135
 136 static int __init dummy_init_module(void)
 137 {
 138         int i, err = 0;
 139
 140         rtnl_lock();
 141         err = __rtnl_link_register(&dummy_link_ops);
 142
 143         for (i = 0; i < numdummies && !err; i++)
 144                 err = dummy_init_one();
 145         if (err < 0)
 146                 __rtnl_link_unregister(&dummy_link_ops);
 147         rtnl_unlock();
 148
 149         return err;
 150 }
 151
 152 static void __exit dummy_cleanup_module(void)
 153 {
 154         rtnl_link_unregister(&dummy_link_ops);
 155 }
 156
 157 module_init(dummy_init_module);
 158 module_exit(dummy_cleanup_module);
 159 MODULE_LICENSE("GPL");
 160 MODULE_ALIAS_RTNL_LINK("dummy");